Poly(aryl ether ketones) are a known class of engineering polymers. Several poly(aryl ether ketones) are highly crystalline with melting points above 300.degree. C. Two of these crystalline poly(aryl ether ketones) are commercially available and are of the following structure. ##STR1##
Over the years, there has been developed a substantial body of patent and other literature directed to formation and properties of poly(aryl ethers) (hereinafter called "PAE"). Some of the earliest work, such as by Bonner, U.S. Pat. No. 3,065,205, involves the electrophilic aromatic substitution (e.g., Friedel-Crafts catalyzed) reaction of aromatic diacyl-halides with unsubstituted aromatic compounds such as di-phenyl ether. The evolution of this class to a much broader range of PAE's was achieved by Johnson et al., Journal of Polymer Science, A-1, vol. 5, 1967, pp. 2415-2427; Johnson et al., U.S. Pat. Nos. 4,107,837 and 4,175,175. Johnson et al. show that a very broad range of PAE's can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol. By this method, Johnson et al. created a host of new PAE's including a broad class of poly(aryl ether ketones), hereinafter called "PAEK'S".
In recent years, there has developed a growing interest in PAEK's as evidenced by Dahl, U.S. Pat. No. 3,953,400; Dahl et al., U.S. Pat. No. 3,956,240; Dahl, U.S. Pat. No. 4,247,682; Rose et al., U.S. Pat. No. 4,320,224; Maresca, U.S. Pat. No. 4,339,568; Atwood et al., Polymer, 1981, vol. 22, August, pp. 1096-1103; Blundell et al., Polymer, 1983, vol. 24, August, pp. 953-958, Atwood et al., Polymer Preprints, 20, No. 1, April 1979, pp. 191-194; and Rueda et al., Polymer Communications, 1983, vol. 24, September, pp. 258-260. In early to mid-1970, Raychem Corp. commercially introduced a PAEK called Stilan.RTM., a polymer whose acronym is PEK, each ether and keto group being separated by 1,4-phenylene units. In 1978, Imperial Chemical Industries PLC (ICI) commercialized a PAEK under the trademark Victrex PEEK. As PAEK is the acronym of poly(aryl ether ketone), PEEK is the acronym of poly(ether ether ketone) in which the 1,4-phenylene units in the structure are assumed.
Thus, PAEK's are well known; they can be synthesized from a variety of starting materials; and they can be made with different melting temperatures and molecular weights. The PAEK's are crystalline, and as shown by the Dahl and Dahl et al. patents, suora, at sufficiently high molecular weights they can be tough, i.e., they exhibit high values (&gt;50 ft-lbs/in.sup.2) in the tensile impact test (ASTM D-1822). They have potential for a wide variety of uses, but because of the significant cost to manufacture them, they are expensive polymers. Their favorable properties class them in the upper bracket of engineering polymers.
PAEK's may be produced by the Friedel-Crafts catalyzed reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether as described in, for example, U.S. Pat. No. 3,065,205. These processes are generally inexpensive processes; however, the polymers produced by these processes have been stated by Dahl et al., supra, to be brittle and thermally unstable. The Dahl patents, supra, allegedly depict more expensive processes for making superior PAEK's by Friedel-Crafts catalysis. In contrast, PAEK's such as PEEK made by nucleophilic aromatic substitution reactions are produced from expensive starting fluoro monomers, and thus would be classed as expensive polymers.
These poly(aryl ether ketones) exhibit an excellent combination of properties; i.e., thermal and hydrolytic stability, high strength and toughness, wear and abrasion resistance and solvent resistance. Thus, articles molded from poly(aryl ether ketones) have utility where high performance is required.
As indicated earlier, poly(aryl ether ketones) are highly crystalline materials with melting points well above 300.degree. C. They are melt-fabricated at temperatures that are at least 360.degree. C.; more often, however, temperatures of 400.degree. C. to 430.degree. C. are required for successful molding or extrusion. Hence, if the full potential of this very unique class of polymers is to be realized, the poly(aryl ether ketone) melt must be stable at the above high temperatures for periods of up to 30 minutes.
Unstabilized PAEKs show a strong tendency to crosslink in the melt. The behavior is highly undesirable since it leads to degradation of polymer properties and an increase of its melt viscosity. As the exposure time in the melt lengthens, melt fabrication becomes progressively more difficult.
Attempts to melt-stabilize poly(aryl ether ketones) were made by others. Thus, U.S. Pat. No. 3,767,620 claims that PAEK's can be stabilized by treatment with a chemical reducing agent in an acidic environment. Representative reducing agents cited in the patent included primary and secondary alkanols in combination with hydrogen chloride; formic acid; and silanes, e.g., trialkylsilanes such as triethylsilane. Interestingly enough, the use of formic acid led, in our hands, to complete gellation of the polymer.
Inorganic stabilizers, e.g., amphoteric metal oxides ( .gamma.-Al.sub.2 O.sub.3) or molecular sieves are described in U.S. Pat. Nos. 3,925,307 and 4,593,061. Along related lines, non-hydrolyzable divalent metal oxides or sulfides, such as zinc oxide or zinc sulfide, were shown to be good stabilizers for poly(aryl ether sulfones)--see U.S. Pat. No. 3,708,454.
British Patent No. 1,446,962 and U.S. Defensive Publication No. T 948,008 disclose the use of phosphorus containing stabilizers of the general formula (3); it ##STR2## is indicated that the addition of from about 0.01 to about 4.0 percent by weight of (3) to a poly(aryl ether ketone) reduces the tendency of the melt viscosity of the polyketone to increase upon prolonged heating. In formula (3), n is 0 or 1 and each of Q', Q" and Q'" is --R or --OR, where R is a monovalent hydrocarbon radical containing up to 20 carbon atoms. Our own investigation (see "Experimental") has shown that the use of some organic phosphorus compounds described by formula (3) has very little effect on the melt viscosity of PAEK's; in fact, in some instances (cf. phosphonites) a negative effect is observed, i.e., the viscosity actually increases. In other instances, phosphites did lead to improvements, but the latter were erratic.